Lead screws translate rotary motion from a motor or the like into linear motion through a nut. The motor, lead screw and nut form a lead screw assembly. Since lead screws have large surface areas there is considerable friction between a lead screw and a nut that engages the lead screw and converts the rotational motion of the lead screw into linear motion. Such friction is overcome by lubrication, usually with oil.
Exemplary of the prior art is U.S. Pat. No. 6,220,110 that shows a lead screw having oil lubrication using a ball recirculation block with oil storing means wherein a cavity in the ball recirculation block which being not effectively used for circulating balls is utilized for storing lubrication oil. An oil exuding hole is provided to communicate with the oil stored cavity and a turning passage for balls so as to lubricate the moving balls. In order to prevent the lubrication oil remained at a standstill in a certain region in the cavity by its own gravity from failing to lubricate the balls, there is provided an oil containing element with a plurality of oil absorbing and distribution branches to lubricate the balls just passing by the turning passage. Furthermore, the ball recirculation block is formed of two pieces of plastic members bonded by supersonic wave bonding technique so as to achieve reduction of manufacturing cost and ensure perfect oil sealing effect of the ball recirculation block.
In U.S. Pat. No. 6,023,991 a lead screw of the ball follower type is shown to have a screw shaft, a ball screw nut, a plurality of balls contained in the ball screw nut which is in threadable engagement with the shaft so that it is capable of relative movement in the linear axial direction as guided by the rolling of the balls, and a lubricant-containing polymer member that is installed in the ball screw nut in contact with the balls or in slidable contact with screw grooves in the screw shaft. The lubricant seeps out of the polymer member slowly and is supplied not only to the balls but also to the screw grooves, so that it maintains the desired lubricating effect in a consistent and automatic way over an extended period of time.
In U.S. Pat. No. 6,752,245 a ring-like lubricant supply device is shown to be fitted into a recess of a nut member. The lubricant supply device contains a lubricant and is formed in an outer peripheral surface with notches. Tubular members each having an outer diameter larger than the diameter of the notch are inserted into the notches, pushing and widening the notches in a circumferential direction. One end of the tubular member is fitted into a recess of a retaining ring and the retaining ring is fixed to a nut member.
In FIG. 1, a prior art lead screw 11 is shown to be axially driven by a stepper motor 13. The lead screw carries a load member 15 wherein precisely measured rotational motion of the screw 11 translates to precise linear motion of load member 15. The 3-piece nut 17 has first and second members 21 and 23 with internal threads driven by the screw 11. The two members are separated by an annular spacer 25 in a well-known anti-backlash configuration. The annular spacer does not contact the lead screw but has portions surrounding tubular extensions of the first and second members 21 and 23. Lubrication is applied directly to the lead screw and the nut tends to push lubricants to opposed ends of the screw where it does no good.
Thus, one of the problems in prior art lead screw lubrication is that excess lubricant is forced toward opposed distant ends of the lead screw, eventually piling up at the ends. An object of the invention was to provide lead screw lubrication with improved anti-friction qualities while preventing excess lubricant from endwise build up.